An argument between rival gang members led to the shooting of three people Saturday in Civic Center Park, where tens of thousands of people had gathered for the largest marijuana smokeout in the country, Denver police said Monday.

Detectives interviewed a "person of interest" who was seen in a YouTube video walking around the fleeing crowds but released him without arrest. Police had described the unidentified man as an accomplice to the "primary suspect," for whom detectives continued to search.

Police described the second man only as black, about 6 feet tall and 180 pounds. He was wearing a light blue baseball cap and a gray hooded sweatshirt during the shooting, which happened near the amphitheater about 5 p.m., as crowds were starting to trickle out of the park.

Police spent the ensuing hours combing through videos posted on YouTube as well as surveillance from nine overhead cameras posted in the vicinity of the park.

But it was unclear if they had viewed footage of the shooting itself.

"I don't know that we have that," department spokesman Sonny Jackson said. "If someone does have that, we'd love to get it from them."

It was the second time in less than a year that gang gunfire pierced a large gathering. Denver police Officer Celena Hollis was killed last summer when Rollin Oliver, apparently fleeing a group of Crips, opened fire in a crowded jazz concert at City Park. Oliver pleaded guilty to second-degree murder earlier this month.

"These large events have been grounds for tension among certain groups," said the Rev. Leon Kelly, who runs Open Door Youth Gang Alternatives.

He had concerns about the 4/20 rally because of the recent building tension. Gang members often come to gatherings armed for protection, which makes even unplanned run-ins with rivals more dangerous and volatile.

"People don't think their safety is in jeopardy because they don't know what's going on in the hood. There's a false sense of security that exists. They just figure, who's going to shoot in a park in the light of day?"